Smoke detectors which are installed, for example in an aircraft toilet or in a freight space or in crew rest areas, must be monitored and checked frequently to assure their proper function when it becomes necessary to detect smoke. Particularly, it is necessary to monitor an air flow passage that leads to an air inlet of a smoke detector so that smoke can reach the detector. The air flow passage leading to the smoke detector inlet must not be clogged or otherwise obstructed by being covered, pasted up or otherwise contaminated so that air and thus smoke can reach the inlet opening of the smoke detector. The smoke detector cannot work if the smoke cannot get to the smoke detector. This clogging may, for example, occur in a protective screen or grid structure that is positioned in the air flow passage to the detector, whereby the function of the smoke detector would be impaired or even prevented.
It is necessary in all aircraft which by law must be equipped with smoke detecting devices, to regularly visually inspect these devices, for example in accessible areas such as toilets, crew rest areas or the like. These regular inspections must be made by the crew and must be done frequently, for example every 15 minutes, particularly on long distance flights. The check must make sure that the air flow passage or passages leading to the smoke detector are not obstructed. Thus, it is conventional to ascertain by an exclusively visual inspection whether the smoke detectors in the aircraft are prevented from functioning properly, for example by obstructions that may be a freight container that has been positioned in front of the air inlet and thus of the smoke inlet leading to the smoke detector. In areas in which unfiltered air is circulating such as in a freight space, the air flow passage leading to a smoke detector may be obstructed or even completely blocked quite quickly, which leads to impairing or even preventing the proper function of the smoke detector.